Microsatellite and STR

Paternity testing using microsatellite markers is one of the most reliable and widely used methods of DNA analysis. Microsatellites are areas of concentrated short base sequences (usually two to six bases) that are repeated in a DNA sequence. The number of these repeats varies from individual to individual, making them suitable for personal identification andproof of parent-child relationships.

What are microsatellite markers?

• Microsatellites, also called Short Tandem Repeats (STRs), are short repeat sequences located at specific positions on the genome.
• These repeat sequences are very useful in creating individual DNA profiles because of the different patterns among individuals.
• For example, if one person has 10 repetitions of “AT” and another has 12, this difference is used to determine personal identification and parent-child relationships.

Use of Microsatellite Markers in Paternity Tests

In paternity testing, since a child inherits half of his or her DNA from both parents, the child’s microsatellite markers (STRs) are checked to see if they match those inherited from the mother and father, respectively.The process is as follows

1. Collection of DNA samples

• A DNA sample is taken from the person to be authenticated (usually the child, mother, or father).The most commonly used method is to collect cells from the oral cavity with a swab.

2. Amplification of STR region (using PCR method)

• In the paternity test using microsatellite markers, the STR region is amplified using the PCR method; the amplification of the STR region makes it possible to analyze the number of repetitions.

3. Comparison of DNA profiles

• The number of amplified STR repeats is analyzed to see if the markers match between the parent and child.Since children inherit half their DNA from both parents, half of the child’s markers should match the father and the other half should match the mother.

4. Determination of parent-child relationship

• If the results of the test show a very high probability that the STR markers of the child and the father match, the parent-child relationship is proven.The accuracy of the paternity test is usually greater than 99.9%, providing a very reliable result.

Advantages of Parent-Child Relationships Using STR Markers

1. High accuracy: STR markers are very diverse and individual markers are highly discriminating, making them very reliable in proving parent-child relationships.
2. Possible with small amounts of DNA: Microsatellite markers are amplified by PCR, so even small amounts of DNA samples can be analyzed. Parent-child identification is possible even from old materials or small amounts of samples.
3. Rapid Results: Results are available within days to weeks of DNA sample collection, allowing for relatively short turnaround times.
4. Use as legal evidence: Paternity tests using microsatellite markers are often used as legal evidence and are used to prove parent-child relationships in courts of law.

Point of attention

• Sample Quality: Deteriorated DNA samples may result in inaccurate analysis. It is important that samples are clean and well preserved.
• Legal Appraisal: For a paternity test to be legally valid in Japan, it must be conducted at a facility accredited as a legal appraisal.If the test is outsourced overseas, it may not be accepted as legal evidence.

Summary

Paternity testing using microsatellite markers (STRs) is a highly reliable method that can prove paternity with extremely high accuracy. It is widely used not only to prove parent-child relationships, but also for criminal investigations and personal identification, and has been established as a standard method for DNA analysis.

Supervisor of the article

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Dr. Hiroshi Oka

Director of CAP Laboratory

Graduated from Keio University, Faculty of Medicine

Doctor of Medicine

Medical Doctor